Four months after a limited initial launch, Comcast on Thursday expanded its Xfinity Mobile service to all Xfinity internet customers across the U.S., with some other limitations in tow —most notably that people buy or rent a new phone.

An iPhone 7, for instance, is $649.99 paid in full, or $27.08 per month for two years. If a person doesn't maintain at least one Xfinity service, a device's full price will be charged. The company is also offering the 7 Plus, SE, and 6s/6s Plus.

The Mobile service itself automatically switches between Comcast Wi-Fi hotspots and the Verizon network. Two subscription tiers are available —a $45 "unlimited" plan, with throttling after 20 gigabytes, or a $12-per-gigabyte option which is cheaper only if people stay under 3 gigabytes.

The arrangement is similar in some respects to Google's Project Fi, which likewise depends on a mix of Wi-Fi and third-party cellular with per-gigabyte data. Fi doesn't demand any other Google service, but also doesn't offer an unlimited plan, and does require one of four Google-branded phones.

It's as yet unknown if Comcast is planning to carry Apple's rumored "iPhone 8", "iPhone 7s," and/or "7s Plus" at launch. In the U.S. Apple typically prioritizes its own stores, followed by the four major national carriers: AT&T, Verizon, T-Mobile, and Sprint.